Pretreatment of dehydrogenation feeds with group viii metal oxides

ABSTRACT

A process for removing dehydrogenation catalyst poisons from paraffin and steam feedstreams by pretreating the feedstreams with Group VIII metal oxides. Undesirable silica is removed from turbo-electric generator steam feedstreams through the process of pretreating said steam with Group VIII metal oxide.

United States Patent 1 Drehman et al.

[451 Sept. 25, 1973 PRETREATMENT OF DEHYDROGENATION FEEDS WITH GROUP VIII METAL OXIDES [75] Inventors: Levvis E. Drehman; Floyd E. Farha,

Jr.; Marvin M. Johnson, all of Bartlesville, Okla.

[73] Assignee: Phillips Petroleum Company,

Bartlesville, Okla.

[22] Filed: June 16, 1971 [21] Appl. No.: 153,821

[52] [1.8. CI. 260/683.3, 208/88 R, 208/137 R [51] Int. Cl. C070 5/18 [58] Field of Search 260/683.3; 208/137,

[56] References Cited UNITED STATES PATENTS 2,500,146 3/1950 Fleck et a1. 260/137 3,531,543 9/1970 Clippinger et a]. 260/6833 FOREIGN PATENTS OR APPLICATIONS 454,668 4/194] Canada 260/6833 OTHER PUBLICATIONS Kalichevsky Chemical Refining of Petroleum 1962 Page 34.

Primary Examiner-Delbert E. Gantz Assistant Examiner.l. M. Nelson Att0rney.l. Arthur Young et al.

[ 5 7 ABSTRACT 7 Claims, No Drawings PRETREATMEN'I F DEI-IYDROGENATION FEEDS WITII GROUP VIII METAL OXIDES This invention relates to a process for removing catalyst poisons from dehydrogenation feedstreams. In another aspect, the invention relates to an improved dehydrogenation process. In yet another aspect, the invention relates to a process for removing silica from steam.

It is conventional in the dehydrogenation of paraffins to utilize catalysts such as nickel-kieselguhr, chromium oxide-alumina, zinc oxide alumina, platinum-alumina, and the like. Additionally, a platinum catalyst on a support such as zinc aluminate is known to be one possible catalyst for the dehydrogenation of paraffins in the presence of steam and oxygen. Specifically, the catalytic effect of many Group VIII metals is known when deposited on a support of alumina, silica, Group II aluminate spinel, and the like; and alkalized by the use of alkali or alkaline earth metal.

The group of metals referred to herein are as classified in the Periodic Table published by the Chemical Rubber Companys Handbook of Chemistry and Physics, 45th Edition (1964), page B-2. Dehydrogenation of a hydrocarbon feedstream by contacting same with a fixed bed of catalyst material is known in the art. It is further'known in the art that feedstocks to be dehydrogenated often contain relative small amounts of materials which are poisonous to the dehydrogenation catalyst, resulting in frequent shutdowns in order to regenerate or replace the poisoned catalyst. We have now discovered an advantageous process for promoting longer life in dehydrogenation catalysts whereby the feedstream to be dehydrogenated is passed before contact with the dehydrogenation catalyst into contact with a Group VIII metal oxide.

Accordingly, it is an object of this invention to provide a process for removing dehydrogenation catalyst poisons from dehydrogenation feedstreams. It is another further object of our invention to provide a process for extending the useful life of a dehydrogenation catalyst system. It is a further object of our invention to provide a process for removing silica from steam through the use of Group VIII metal oxides. Other aspects, objects and the several advantages of our invention will be apparent from this description, and the appended claims.

According to our invention, a dehydrogenation catalyst is given longer process life by pretreating dehydrogenation feedstreams with Group VIII metal oxides. In the dehydrogenation of paraffin-steam feedstreams, catalyst deactivation is readily deferred through the use of a Group VIII metal oxide guard chamber. For example, zinc aluminate, promoted with platinum and tin, is a satisfactory catalyst for the dehydrogenation of paraffins in the presence of steam. In two tests directed toward determining the life of the aforementioned catalyst, it was determined and demonstrated that the catalysts had a life of about 4% months. An accelerated life test was established in which a small portion of the catalyst was operated under severe conditions. At these conditions, a small portion of the catalyst became almost completely deactivated with 72 hours. It was discovered that a bed of Group VIII metal oxides, for example, iron oxide Fe,o,) immediately ahead of the catalyst bed removed poisons from the paraffin-steam feedstreams in such efficiency that the catalysts showed virtually no deactivation for at least 288 hours. These findings are recorded herein below in Examples 1-111 and Table I.

The catalytic dehydrogenation system of this invention is particularly well adapted to the dehydrogenation of paraffins comprised of aliphatic compounds having from 2 to about 12 carbon atoms per molecule. In one embodiment of the invention, n-butane is dehydrogenated to butene and butadiene containing product. The catalyst systems of this invention are employed at temperatures between 600 and 1,300 F., preferably between 800 and 1,l00 F, and at total pressures in the range of 0 to 500 psig, preferably 50 to 350 psig. Steam-to-hydrocarbon mole ratios of 0.5:1 to 30:1, preferably 2.5:1 to 20:1 are employed. Total space velocity (GI'ISV) of hydrocarbon and steam is between and 50,000, preferably between 500 and 20,000 volumes of gas per volume of catalyst per hour (32 F, 0 psig pressure).

It was also discovered that in addition to the use of iron oxide as a means of extending dehydrogenation catalyst life, other Group VIII metal oxides, for example, cobalt oxide and nickel oxide, canalso be used. It is believed that silica is the catalyst poison removed by the iron-oxide pretreatment bed, therefore any metal oxide capable of reacting with silica may be used. The use of these pro-treatment oxides (iron oxide) would also find utility in purifying steam used in high pressure turbo-electric generators in avoiding deposits of silica on turbine blades.

In the catalytic dehydrogenation of paraffins in the presence of steam, catalyst poisons such as silica can be found in varying amounts of both paraffins and steam feedstreams. Therefore, either the steam or paraffin feedstream can be individually pretreated before being combined and introduced to the dehydrogenation catalyst. However, a guard chamber can be located upstream of the catalyst bed, and both the paraffins and steam will pass through the guard chamber containing the iron oxide (Fe O The following examples provide a more complete understanding of the invention and are not to be limiting upon the scope of same. Examples I through Ill contain data which fully illustrate the advantages of using iron oxide as the guard chamber material. Example Ill utilizes Fe O as the guard chamber material as compared to AI O as used in Example I, and ZnAl- 0 SnO as used in Example II. Theguard chamber material in each case was charged to the reactor immediately atop the catalyst. The reactor and guard chamber was comprised of a l/4-inch stainless steel tube with an inside diameter of 0.31 inches. The catalyst used had a volume of 1.27 cubic centimeters The volume of guard chamber material used was 8 cubic centimeters of A1 0 in Example I, 6 cubic centimeters of ZnAI O. 2 cubic centimeters of Sn0 Example II, and 8 cubic centimeters of Fe 0 as used in Example III. The feed (pure grade normal butane) and steam' was downflowed so that the feedstream contacted the guard chamber material before contacting the catalyst. The guard chamber material was at the same temperature as the catalyst. Exemplary flow rates, temperature, pressure, and other physical conditions are hereinafter included in the three examples listed below.

Example I 2 Example II 1 Example III 2 Guard chamber material aAlzOg ZilAlzOri-SnOz F8103 Catalyst preparation: 1

Weight percent Pt 0. 4 0.2 0. 2

Weight ercent Sn 0. 4 0. 2 0.4

Weight cuta yst charged g.. l. 35 1.35 1.35

Average feed rate, nsv a, no s, 410 1. .150

Tcinperature, 1,100 L100 1,100

Pressure, p.s.i.g t I00 I00 100 Average steam mole ratio. 8. 6 J. 0 10. 4

Percent Percent Percent IIrs. total conv it com k eonv. k

8-16 it 0 2,385 16. 2 5, 405 ill. 0 0,035

l6-24 8. it i, 500 14.0 5.085 18.1 6, U

1 Preparation of butane a. Slurry an aqueous mixture mixing. b. Dry, grind and tablet. c. Calcine tablets at 1,800 F. for 3-8 hours. 1. Regriud and screen to desired mesh sizc.

dehydrogenation catalyst:

oi ZnO and Alon A120; in a ball mill to achieve intimate e. Impregnate with aqueous solution of chloi'platinie acid and stannous chloride.

Xe=equilibrium conversion determined by temperature and partial pressure of butane.

Xe is approximately 0. 6 in these tests. X =observed conversion of butane.

The above examples illustrate that when using the Al,0 guard chamber material of Example I, the catastream by contacting said feedstream under suitable dehydrogenation conditions in a first zone with a catalytic dehydrogenation process percent conversion was lyst comprising a platinum and tin promoted zinc alurcduced to half within 48 to 56 hours. The ZnAl,O SnO guard chamber material of Example experienced a similar decline in percent conversion after 88 to 96 hours. The Fc O guard chamber material of Example lll experienced less than a 20 percent reduction in the percent conversion feature after operating from 192 to 200 hours. Since Example II utilized a guard chamber material very similar to the actual catalyst. the advantages of using Fe- O as a guard chamber material is selfevident.

A typical product composition, gas-phase product by mole percent is presented in Table I below.

(I) added for flushing purposes. Reasonable variation and modification are possible minate in the presence of steam, the improvement extending the useful life of said catalyst which comprises passing at least one of said feedstream and said steam into contact with a Group VIII metal oxide in a second zone prior to the introduction of said at least one of said feedstream and said steam into said first zone, the material thus passed into contact with said Group VIII metal oxide containing silica which is poisonous to said catalyst, to thereby at least partially remove said silica 0 from said at least one of said feedstream and said steam within the scope of this disclosure, the essence of which is that there is provided a dehydrogenation process wherein a feedstream consisting essentially of parrafins-steam is pro-treated in the presence of a Group VIII metal oxide for the purposes of removing dehydrogenation catalyst poisons. Modifications and variations before the contacting thereof with said catalyst.

2. A process in accordance with claim 1 wherein said steam and said feedstream are admixed, the resulting admixture is passed through said second zone in contact with said Group VIII metal oxide, and the thus treated admixture is then passed into said first zone for contact with said catalyst.

3. A process according to claim 2 wherein the Group VIII metal oxide is selected from the group consisting of iron, cobalt, and nickel oxides.

4. A process according to claim 2 wherein the Group VIII metal oxidc is iron oxide having the formula Fe O 5. A process according to claim 2 wherein the paraffin feedstream is comprised of aliphatic compounds having from two to about 12 carbon atoms per molecule.

6. A process according to claim 5 wherein the aliphatic compounds are comprised of butane.

7. A process according to claim 4 wherein the mole ratio of steam to paraffinic material in said second zone is in the range of about 0.5:1 to about 30:1, wherein the total space velocity of said admixture is in the range of about to about 50,000 volume of gas (32 F, O psig) per volume of said catalyst per hour, wherein the temperature in said first zone is in the range of about 600 to about l,300 F, and wherein the pressure in said first zone is in the range of about 0 to about 500 psig. 

2. A process in accordance with claim 1 wherein said steam and said feedstream are admixed, the resulting admixture is passed through said second zone in contact with said Group VIII metal oxide, and the thus treated admixture is then passed into said first zone for contact with said catalyst.
 3. A process according to claim 2 wherein the Group VIII metal oxide is selected from the group consisting of iron, cobalt, and nickel oxides.
 4. A process according to claim 2 wherein the Group VIII metal oxide is iron oxide having the formula Fe2O3.
 5. A process according to claim 2 wherein the paraffin feedstream is comprised of aliphatic compounds having from two to about 12 carbon atoms per molecule.
 6. A process according to claim 5 wherein the aliphatic compounds are comprised of butane.
 7. A process according to claim 4 wherein the mole ratio of steam to paraffinic material in said second zone is in the range of about 0.5:1 to about 30:1, wherein the total space velocity of said admixture is in the range of about 100 to about 50,000 volume of gas (32* F, O psig) per volume of said catalyst per hour, wherein the temperature in said first zone is in the range of about 600* to about 1,300* F, and wherein the pressure in said first zone is in the range of about 0 to about 500 psig. 